The invention relates to a method for checking ordered cigarette groups corresponding to the content of a cigarette pack with an electro-optical checking element, preferably a CCD linear array chip or a CCD camera, connected to a signal data processing arrangement, for the measurement of the intensity of light reflected by filter-side ends of the cigarettes. Furthermore, the invention relates to a method for checking ordered cigarette groups corresponding to the content of a cigarette pack with an electro-optical checking element, preferably a CCD camera, connected to a signal data processing arrangement, for the measurement of the intensity of reflected light, a measurement zone preferably formed from pixels of the checking element being assigned to at least one partial area of the ends of the cigarettes.
High-performance machines are required to produce cigarettes and fill cigarette groups in cigarette packs. Despite careful manufacturing, however, it is often the case that the cigarette packs that have been produced and delivered to the customer have cigarettes missing or contain cigarettes inadequately filled with tobacco. When selecting checking methods for separating out such defective cigarette groups, it has to be taken into account that the checking must take place in a fast, continuous or batchwise conveying process.
In a checking method used previously, an ordered cigarette group corresponding to the content of a cigarette pack is moved past a checking device in which the intensities of reflected light which are measured by a CCD camera are statistically evaluated.
The invention is based on the object of proposing an improved, contactless checking method for monitoring that cigarette groups are complete and/or that the cigarettes are filled with tobacco.
In order to achieve this object, the method according to the invention is characterized in that a measurement zone formed by the checking element, preferably by the pixels of the CCD linear array chip or the CCD camera, is assigned to the ends of the cigarettes and the cigarette interspaces formed between the latter, at least partial areas of the measurement zone, in particular pixels of the CCD camera or of the CCD linear array chip, are arranged in curved or rectilinear, in particular horizontal or vertical, evaluation bars, and the measurement signal measured along the evaluation bars is evaluated in the signal data processing arrangement in order to check that the cigarette group is complete.
The measurement element for checking the cigarette groups thus operates contactlessly on the basis of a CCD linear array chip or a CCD camera, so that the cigarette group can be checked even with a fast conveying cycle. In this case, the measurement element can be arranged at any desired point in the conveying process as long as the ends of the cigarette groups are freely accessible in this. By way of example, the checking can be carried out during the conveying process in a pocket conveyor. A further possibility is for the cigarette groups to be checked in a folding turret.
According to the invention, in a further refinement with regard to the evaluation of the intensity profile yielded by the CCD camera or the CCD linear array chip, the method is characterized in that the number of cigarettes in the region of the evaluation bar or bars is determined from a count of the crossings of the intensity profile through a threshold value with the threshold value subsequently being exceeded and/or undershot. This evaluation method is based on the fact that the reflected light in the region of the light filter areas of the cigarettes is greater than the intensity measured in the region of the dark cigarette interspaces formed by adjacent cigarettes. A rise in the measured intensity profile can thus be evaluated as a transition from a cigarette interspace to a filter-side end of a cigarette. If a cigarette is missing in a row of cigarettes, the number of times that the high intensity is reached in the region of the filter areas is thus one fewer than in the case of a complete row of cigarettes. This is detected from the count of the crossings of the intensity profile through a threshold value.
If a cigarette is missing within a cigarette group with a plurality of rows of cigarettes, adjacent cigarettes are displaced. The consequence of this is that the distance between the first and last cigarettes in a row of cigarettes is reduced on account of a cigarette being missing. Therefore, a further method according to the invention is characterized in that the completeness of the cigarette group is determined from the comparison of the distance between the first and last crossings of the intensity profile through a threshold value with a desired value.
The number of high measured intensity values increases with the number of filter-side end areas of the cigarettes in the region of the evaluation bar of the CCD linear array chip or CCD camera. Accordingly, in a further method according to the invention, the area, determined in particular by summation of the intensity values measured along the evaluation bar, underneath the curve of the measured intensity signal can be compared with a desired value determined for the complete cigarette group.
In order to achieve the object, a further method according to the invention is characterized in that a measurement signal measured in the pixels assigned to the ends of the cigarettes and also the cigarette interspaces is evaluated in accordance with the horizontal and vertical positions of the pixels as a two-dimensional measurement zone.
In a three-dimensional representation of the measured intensity against the horizontal and vertical positions of the pixels in the two-dimensional measurement zone, the intensity profile can thus be represented as a curved area having high plateaus in the region of light cigarette areas, for example in the region of the light end areas of the cigarettes, and valleys for the regions with low measurement intensities, for example in the region of the cigarette interspaces.
In a method according to the invention, this relief-like changeover of mountains with high plateaus and valleys is evaluated in such a way that, in the case where the measurement zone is arranged on the tobacco side, the presence of a large number of small adjacent intensity values is used as an indicator of recesses in the filling of the cigarettes with tobacco. In this checking method, therefore, valleys, that is to say a real regions with small adjacent intensity values, are deliberately sought. In the region of a valley, an a real shadow region is present at the tobacco-side end of the cigarette. This can be assessed as an indicator of recesses in the filling of the cigarettes, so-called voids.
If a cigarette is missing from a cigarette group and the cigarettes are checked in the region of the filter-side end areas of the cigarettes, the fact that a cigarette is missing from the cigarette group has the consequence that a xe2x80x9cvalleyxe2x80x9d with low measurement intensities is present in the region at which a plateau with high intensity should be present for a complete cigarette group. Therefore, in the region of the desired positions of the end filter areas, a large number of low measurement intensities are measured instead of a large number of adjacent high measurement intensities. In the case of the determination of the frequency distribution of the measured values with measurement intensities within predefined intensity classes, the occurrence of a large frequency in conjunction with large measurement intensities indicates the presence of a light filter area, while the presence of large frequencies in conjunction with small measurement intensities can be evaluated as an indicator of a dark cigarette interspace. Further methods relate to preferred refinements of the invention.